PROJECT SUMMARY/ABSTRACT There is a fundamental gap in our knowledge to explain the origin of prostate cancer (PCa). Unlike many cancers, PCa lacks signature mutations in key oncogenes and tumor-suppressor genes and, instead, displays large-scale genomic instability. We propose to study subcellular organelle instability as a mechanism that results in genomic instability in epithelial cells of the prostate gland. Specifically, we focus on centrosomes, tiny cytoplasmic organelles that dramatically influence genome integrity. Centrosomes can become subcellular pathognomonic structures when they are amplified, as is the case in many different cancers, causing mitotic errors, genomic instability and inducing tumorigenesis in mouse models. Likewise, centrosome loss causes mitotic errors and genomic instability identical to centrosome amplification, but has not been reported in cancer. We discovered recently that human prostate adenocarcinoma lack centrosomes, providing a novel mechanistic explanation for genomic instability in PCa. Our long-term goal is to discover the abnormal changes that underlie prostate tumorigenesis, malignancy and recurrence, and to improve PCa diagnosis and treatment strategies. The objective of this application is to determine the contribution of centrosome loss in driving genomic instability resulting in PCa and to determine the molecular mechanistic basis for centrosome disappearance. Drawn from our preliminary data, our central hypothesis is that hypoxia is a key physiologically-relevant determinant of centrosome loss in the prostate which, in turn, stimulates genomic instability and tumorigenesis. The rationale for the proposed research is to address the provocative question of how cancer-specific changes in subcellular pathognomonic structures (specifically, centrosome loss) transpire and contribute to carcinogenesis. This hypothesis will be tested in three specific aims: 1) Determine whether centrosome loss is triggered by hypoxia in prostate cells and tumors; 2) Determine whether centrosome loss drives genomic instability in normal prostate epithelial cells and promotes tumorigenesis; and 3) Determine if centrosome loss is characteristic of high-grade prostatic intraepithelial neoplasia (PIN, carcinoma in situ). The approach is innovative because it investigates a novel mechanism of subcellular organelle instability during prostate tumorigenesis: specifically, that hypoxia and centrosome biogenesis are mechanistically coupled as drivers of genomic instability in prostate tumor formation. The proposed research is significant because it tests a new concept that the loss of a critical subcellular organelle is responsible for PCa genomic instability, which is both a hallmark and agent of prostate tumor evolution. If we are correct, centrosome loss will be a tangible event early in the genesis of human prostate cancer, providing new early detection and treatment strategies.